Epitaxial structure

ABSTRACT

An epitaxial structure including an epitaxial substrate, a first buffer layer, a first pattern mask layer, a second buffer layer and a second pattern mask layer. The first buffer layer is disposed on the epitaxial substrate. The first pattern mask layer is disposed on the first buffer layer. The second buffer layer is disposed on the first pattern mask layer and a part of the first buffer layer. The second pattern mask layer is disposed on the second buffer layer. A projection of the first pattern mask layer projected on the first buffer layer and a projection of the second pattern mask layer projected on the first buffer layer cover at least 70% of the total area of the first buffer layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 103134380, filed on Oct. 2, 2014. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an epitaxial structure, and particularlyrelates to an epitaxial structure having fewer defects.

2. Description of Related Art

Light emitting diodes (LED) are semiconductor devices manufactured byusing compound (e.g., gallium nitride, gallium phosphide, and galliumarsenide) containing semiconductor materials in a Group III-V element. Alifetime of the LEDs may be as long as 100,000 hours. In addition, theLEDs have the advantages of a quick responding speed (approximately 10⁻⁹seconds), smaller size, lower power consumption, low pollution, highreliability, as well as the capability for mass production. Thus, theLEDs are broadly used in many fields. For example, LEDs are used inluminaires, traffic signal lamps, cell phones, scanners, and faxmachines.

Taking the gallium nitride semiconductor for example, in themanufacturing process of the gallium nitride semiconductor, due to thedifferences in lattice constant and thermal expansion coefficient (CTE)between the semiconductor layer and a hetero-substrate, misfitdislocations and the thermal stress caused by CTE mismatch of thesemiconductor in the epitaxial process are commonly found. Therefore,the conventional nitride semiconductor may be severely bent due to thestress and the chance of generating cracks is thus increased.

SUMMARY OF THE INVENTION

The invention provides an epitaxial structure having fewer defects.

An epitaxial structure of the invention includes an epitaxial substrate,a first buffer layer, a first patterned mask layer, a second bufferlayer, and a second pattern mask layer. The first buffer layer isdisposed on the epitaxial substrate. The first pattern mask layer isdisposed on the first buffer layer. The second buffer layer is disposedon the first pattern mask layer and a part of the first buffer layer.The second pattern mask layer is disposed on the second buffer layer. Aprojection of the first pattern mask layer and a projection of thesecond pattern mask layer projected on the first buffer layer at leastcover 70% of a total area of the first buffer layer.

According to an embodiment of the invention, the projections of thefirst pattern mask layer and the second pattern mask layer projected onthe first buffer layer completely cover the total area of the firstbuffer layer.

According to an embodiment of the invention, a pattern of the firstpattern mask layer and a pattern of the second pattern mask layer arecomplementary to each other.

According to an embodiment of the invention, each of the projection ofthe first pattern mask layer projected on the first buffer layer and theprojection of the second pattern mask layer projected on the firstbuffer layer covers approximately half of the total area of the firstbuffer layer.

According to an embodiment of the invention, a projection of the secondpattern mask layer projected on the first pattern mask layer covers apartial area of the first pattern mask layer.

According to an embodiment of the invention, a nucleating layer disposedbetween the epitaxial substrate and the first buffer layer is furtherincluded.

According to an embodiment of the invention, the nucleating layer is ina monocrystalline structure.

According to an embodiment of the invention, a first type semiconductorlayer, an active layer, and a second type semiconductor layer arefurther included. The first type semiconductor layer is disposed on thesecond pattern mask layer. The active layer is disposed on the firsttype semiconductor layer. The second type semiconductor layer isdisposed on the active layer.

According to an embodiment of the invention, a third buffer layerdisposed between the second pattern mask layer and the first typesemiconductor layer is further included.

According to an embodiment of the invention, materials of the firstpattern mask layer and the second pattern mask layer include siliconoxide or silicon nitride.

According to an embodiment of the invention, a material of the epitaxialsubstrate includes one of sapphire, Si, SiO₂, GaN, AlN, spinnel, SiC,GaAs, LiGaO₂, LiAlO₂, and MgAl₂O₄.

Based on the above, in the epitaxial structure of the invention, thebuffer layers and the pattern mask layers are formed on the epitaxialsubstrate, so that the pattern mask layers are able to block misfitlocations in the buffer layers, so as to reduce a chance that the misfitlocations in the buffer layers extend upward. Then, if a semiconductorlayer is to be stacked on the second pattern mask layer subsequently,the semiconductor layer may have a preferable epitaxial quality.

To make the above features and advantages of the invention morecomprehensible, embodiments accompanied with drawings are described indetail as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a schematic view illustrating an epitaxial structure accordingto an embodiment of the invention.

FIG. 2 is a schematic view illustrating an epitaxial structure accordingto another embodiment of the invention.

FIG. 3 is a schematic view illustrating an epitaxial structure accordingto another embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

FIG. 1 is a schematic view illustrating an epitaxial structure accordingto an embodiment of the invention. Referring to FIG. 1, an epitaxialstructure 100 of this embodiment includes an epitaxial substrate 110, anucleating layer 120, a first buffer layer 130, a first pattern masklayer 140, a second buffer layer 150, and a second pattern mask layer160.

In this embodiment, the epitaxial substrate 110 is a sapphire substrate.However, in other embodiments, any substrate material capable of growinga Group III-V (e.g. a Group III nitride) semiconductor layer (e.g. aGroup III nitride) may be used, such as Si, SiO₂, GaN, AlN, spinnel,SiC, GaAs, LiGaO₂, LiAlO2, or MgAl₂O₄.

The nucleating layer 120 is disposed on the epitaxial substrate 110. Inthis embodiment, the nucleating layer 120 may form in a mono crystallinestructure on the epitaxial substrate 110 through a crystal growthprocess. A material of the nucleating layer 120 may be AlN. However, inother embodiments, the nucleating layer 120 may be formed by asputtering process or by a metal organic chemical vapor deposition(MOCVD) method. Of course, the method and material for forming thenucleating layer 120 are not limited thereto. The nucleating layer 120is formed to decrease a density of defects between the epitaxialsubstrate 110 and semiconductor layers (e.g. the first buffer layer 130,the second buffer layer 150, a first type semiconductor layer 380, anactive layer 382, and a second semiconductor layer 384, as shown in FIG.3) and has a preferable adhesive property, so as to adhere the epitaxialsubstrate 110 and the semiconductor layers. Of course, in otherembodiments, the nucleating layer 120 may be omitted from the epitaxialstructure 100. In this way, the first buffer layer 130 is directlydisposed on the epitaxial substrate 110.

As shown in FIG. 1, the first buffer layer 130 is disposed on thenucleating layer 120, the first pattern mask layer 140 is disposed onthe first buffer layer 130, the second buffer layer 150 is disposed onthe first pattern mask layer 140 and a part of the first buffer layer130, and the second pattern layer 160 is disposed on the second bufferlayer 150.

Since there are significant differences in lattice constant and thermalexpansion coefficient between the Group III-V semiconductor layers andthe epitaxial substrate 110, there may be lattice mismatch as well asmismatch in thermal expansion coefficient. In this embodiment, the firstbuffer layer 130 and the second buffer layer 150 are grown on theepitaxial substrate 110 first, so as to gradually improve an epitaxialquality of the semiconductor layer subsequently stacked on the epitaxialsubstrate 110 by using the first buffer layer 130 and the second bufferlayer 150, thereby preventing a light emitting efficiency of a lightemitting component formed accordingly from being influenced.

It should be noted that due to misfit dislocations, defects D may begenerated in portions of the first buffer layer 130 and the secondbuffer layer 150. As shown by FIG. 1, the defects D in the first bufferlayer 130 and the second buffer layer 150 may extend along a growingdirection (i.e. an upward direction in FIG. 1). To prevent the defects Dfrom continue to extend upward, in this embodiment, the first patternmask layer 140 is disposed on the first buffer layer 130, and the secondpattern mask layer 160 is disposed on the second buffer layer 150. Thefirst pattern mask layer 140 covers a partial area of the first bufferlayer 130 to block some of the defects D extending upward from the firstbuffer layer 130. Some other of the defects D in the first buffer layer130 keep extending upward to the second buffer layer 150. The secondpattern mask layer 160 covers another partial area of the second bufferlayer 150, so as to block the some other of the defects D.

In other words, in the epitaxial structure 100 of this embodiment, thedefects D in the buffer layers 130 and 150 are prevented fromcontinuously extending upward by alternately stacking the pattern masklayers 140 and 160 and the buffer layers 130 and 150 and coveringdifferent positions of the buffer layers 130 and 150 with the patternmask layers 140 and 160. In this way, the semiconductor layerssubsequently stacked on the second buffer layer 150 may have apreferable epitaxial quality. It should be noted that in otherembodiments, the numbers of the buffer layers and pattern mask layersthat are alternately stacked may be three or more respectively, and thenumbers of the buffer layers and the pattern mask layers are not limitedby the above description.

Also, as shown in FIG. 1, in this embodiment, patterns of the firstpattern mask layer 140 and the second pattern mask layer 160 arecomplementary to each other. In an actual manufacturing process, thecomplementary patterns may be manufactured by using a positivephotoresist and a negative photoresist. Of course, in other embodiments,the patterns of the first pattern mask layer 140 and the second patternmask layer 160 may not be complementary to each other, as long asprojections of the first pattern mask layer 140 and the second patternmask layer 160 projected on the first buffer layer 130 at least cover70% of the total area of the first buffer layer 130. In a preferredembodiment, the projections of the first pattern mask layer 140 and thesecond pattern mask layer 160 projected on the first buffer layer 130completely cover the total area of the first buffer layer 130.

In addition, each of the projection of the first pattern mask layer 140projected on the first buffer layer 130 and the projection of the secondpattern mask layer 160 projected on the first buffer layer 130approximately covers half of the total area of the first buffer layer130. However, in other embodiments, it is also possible that an area ofthe projection of the first pattern mask layer 140 projected on thefirst buffer layer 130 is larger or smaller than an area of theprojection of the second pattern mask layer 160 projected on the firstbuffer layer 130. A proportion between the area of the first bufferlayer 130 covered by the projection of the first pattern mask layer 140projected on the first buffer layer 130 and the area covered by theprojection of the second pattern mask layer 160 projected on the firstbuffer layer 130 is not limited to the above description.

It should be noted that while in FIG. 1, an area shielded by the firstpattern mask layer 140 and an area shielded by the second pattern masklayer 160 are alternately distributed, in other embodiments, the firstpattern mask layer 140 may only shield a left portion of the firstbuffer layer 130, while the second pattern mask layer 160 only shields aright portion of the second buffer layer 150. Shapes of patterns andshielding portions of the first pattern mask layer 140 and the secondpattern mask layer 160 are not limited to the above description.

In this embodiment, the first buffer layer 130 and the second bufferlayer 150 include a III-V Group semiconductor such as gallium nitride.Materials of the first pattern mask layer 140 and the second patternmask layer 160 are, for example, silicon oxide. However, in otherembodiments, the materials of the first pattern mask layer 140 and thesecond pattern mask layer 160 may also be silicon nitride. The types ofthe first buffer layer 130, the second buffer layer 150, the firstpattern mask layer 140, and the second pattern mask layer 160 are notlimited to the above description. In addition, in this embodiment, thefirst buffer layer 130 and the second buffer layer 150 may be formed onthe epitaxial substrate 110 by using the metal organic chemical vapordeposition (MOCVD) method, and the first pattern mask layer 140 and thesecond pattern mask layer 160 may be respectively formed on the firstpattern mask layer 140 and the second pattern mask layer 160 by using aplasma enhanced chemical vapor deposition (PECVD) method accompaniedwith a photolithography etching process. However, the methods of formingthe respective layers are not limited to the above description.

FIG. 2 is a schematic view illustrating an epitaxial structure accordingto another embodiment of the invention. Referring to FIG. 2, anepitaxial structure 200 of FIG. 2 differs from the epitaxial structure100 of FIG. 1 in that a projection of a second pattern mask layer 260 ofthe epitaxial structure 200 shown in FIG. 2 projected on a first patternmask layer 240 covers a partial area of the first mask layer 240.Namely, in this embodiment, patterns of the first pattern mask layer 240and the second pattern mask layer 260 are not complementary to eachother. A projection of the second pattern mask layer 260 projected on afirst buffer layer 230 is partially overlapped with a projection of thefirst pattern mask layer 240 projected on the first buffer layer 230 inaddition to covering an area that is not covered by a projection of thefirst pattern mask layer 240 projected on the first buffer layer 230.

Some of the defects D originally close to the first pattern mask layer240 on the first buffer layer 230 but not blocked by the first patternmask layer 240 may already be deviated from the area that is not coveredby the first pattern mask layer 240 when extending upwardly to thesecond buffer layer 250. Thus, in this embodiment, an area covered bythe second pattern mask layer 260 is enlarged, so that the secondpattern mask layer 260 is partially overlapped with the first patternmask layer 240, making these defects D still blocked by the secondpattern mask layer 260.

Similarly, by alternately stacking the pattern mask layers 240 and 260and the buffer layers 230 and 250 in the epitaxial structure 200 andmaking the pattern mask layers 240 and 260 respectively cover at leastdifferent positions of the buffer layers 230 and 250, the defects D inthe buffer layers 230 and 250 are prevented from continuously extendingupward, making the semiconductor layers subsequently stacked on thesecond buffer layer 250 have a preferable epitaxial quality.

FIG. 3 is a schematic view illustrating an epitaxial structure accordingto another embodiment of the invention. Referring to FIG. 3, in thisembodiment, elements the same as or similar to the elements in theepitaxial structure 100 are referred to with the reference numerals ofthe similar or same elements in FIG. 1, and no further details in thisrespect will be further described below. An epitaxial structure 300 ofFIG. 3 mainly differs from the epitaxial structure 100 of FIG. 1 in thatthe epitaxial structure 300 of FIG. 3 further includes a third bufferlayer 370, a first type semiconductor layer 380, an active layer 382,and a second type semiconductor layer 384. The third buffer layer 370 isdisposed on the second pattern mask layer 160 and a part of the secondbuffer layer 150, the first type semiconductor layer 380 is disposed onthe third buffer layer 370, the active layer 382 is disposed on thefirst type semiconductor layer 380, and the second type semiconductorlayer 384 is disposed on the active layer 382.

In this example, the third buffer layer 370 includes a Group III-Vcompound semiconductor such as gallium nitride. The first typesemiconductor layer 380 is, for example, an n-type nitride semiconductorstack layer, and the second type semiconductor layer 384 is, forexample, a p-type nitride semiconductor layer, and the active layer is,for example, multiple quantum wells. The first type semiconductor layer380 and the second type semiconductor layer 384 are, for example, GaN,AlGaN, AlInGaN, or InGaN. An n-type dopant doped in the first typesemiconductor layer 380 may include at least one Group N A element, anda p-type dopant doped in the second type semiconductor layer 384 mayinclude at least one Group II A element. In this embodiment, the n-typedopant may be silicon, and the p-type dopant may be magnesium. However,the types of the n-type and p-type dopants are not limited thereto.

The third buffer layer 370, the first type semiconductor layer 380, theactive layer 382, and the second type semiconductor layer 384 may besequentially formed on the second buffer layer 150 and the secondpattern mask layer 160 by using the metal organic chemical vapordeposition (MOCVD) method. However, manufacture of the third bufferlayer 370, the first type semiconductor layer 380, the active layer 382,and the second type semiconductor layer 384 are not limited thereto. Inother embodiments, the epitaxial structure 300 may also omit the thirdbuffer layer 370. In this way, the first type semiconductor layer 380 isdirectly disposed on the second pattern mask layer 160 and a part of thesecond buffer layer 150. Moreover, in other embodiments, the thirdbuffer layer 370, the first type semiconductor layer 380, the activelayer 382, and the second type semiconductor layer 384 also be formed onthe epitaxial structure 100 of FIG. 2, for example, and are not limitedto the above description.

As shown in FIG. 3, in the epitaxial structure 300 of this embodiment,by using the configuration that the buffer layers 130 and 150 and thepattern mask layers 140 and 160 are alternately stacked on the epitaxialsubstrate 110 and projections of the pattern mask layer 140 and 160projected on any of the buffer layers 130 and 150 completely cover thebuffer layers 130 and 150, the pattern mask layers 140 and 160 are ableto block the defects D in the buffer layers 130 and 150, so as to reducethe chance that the defects D in the buffer layers 130 and 150 extendupward. Thus, the first type semiconductor layer 380, the active layer382, and the second type semiconductor layer 384 formed on the thirdbuffer layer 370 may have a preferable epitaxial quality.

Accordingly to the above, in the epitaxial structure of the invention,the plurality of buffer layers and the plurality of pattern mask layersalternately stacked are formed on the epitaxial substrate, and acombined projection area of the pattern mask layers is capable of atleast covering 70% of the total area of the buffer layers, so as toincrease the chance that misfit dislocations extending upward in thebuffer layers are blocked by the pattern mask layers and thus decrease adensity of misfit dislocations of the whole epitaxial structure. Thus,if a semiconductor layer is to be stacked on the epitaxial structuresubsequently, the semiconductor layer may have a preferable epitaxialquality as well.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. An epitaxial structure, comprising: an epitaxialsubstrate; a first buffer layer, disposed on the epitaxial substrate; afirst pattern mask layer, disposed on the first buffer layer; a secondbuffer layer, disposed on the first pattern mask layer and a part of thefirst buffer layer; and a second pattern mask layer, disposed on thesecond buffer layer, wherein a projection of the first pattern masklayer and a projection of the second pattern mask layer projected on thefirst buffer layer at least cover 70% of a total area of the firstbuffer layer.
 2. The epitaxial structure as claimed in claim 1, whereinthe projections of the first pattern mask layer and the second patternmask layer projected on the first buffer layer completely cover thetotal area of the first buffer layer.
 3. The epitaxial structure asclaimed in claim 2, wherein a pattern of the first pattern mask layerand a pattern of the second pattern mask layer are complementary to eachother.
 4. The epitaxial structure as claimed in claim 3, wherein each ofthe projection of the first pattern mask layer projected on the firstbuffer layer and the projection of the second pattern mask layerprojected on the first buffer layer covers approximately half of thetotal area of the first buffer layer.
 5. The epitaxial structure asclaimed in claim 1, wherein a projection of the second pattern masklayer projected on the first pattern mask layer covers a partial area ofthe first pattern mask layer.
 6. The epitaxial structure as claimed inclaim 1, further comprising: a nucleating layer, disposed between theepitaxial substrate and the first buffer layer.
 7. The epitaxialstructure as claimed in claim 6, wherein the nucleating layer is in amonocrystalline structure.
 8. The epitaxial structure as claimed inclaim 1, further comprising: a first type semiconductor layer, disposedon the second pattern mask layer; an active layer, disposed on the firsttype semiconductor layer; and a second type semiconductor layer,disposed on the active layer.
 9. The epitaxial structure as claimed inclaim 8, further comprising: a third buffer layer, disposed between thesecond pattern mask layer and the first type semiconductor layer. 10.The epitaxial structure as claimed in claim 1, wherein materials of thefirst pattern mask layer and the second pattern mask layer comprisesilicon oxide or silicon nitride.
 11. The epitaxial structure as claimedin claim 1, wherein a material of the epitaxial substrate comprises oneof sapphire, Si, SiO₂, GaN, AlN, spinnel, SiC, GaAs, LiGaO₂, LiAlO₂, andMgAl₂O₄.